1999 DODGE RAM Ignition system

various switch input operations to adjust IAC motor to obtain optimum
idle conditions. Deceleration stall is prevented by increasing airflow
when throttle is closed suddenly.
IGNITION SYSTEM
NOTE: Pickup equipped with 8.0L engine uses Distributorless
Ignition system (DIS). All other models use a Hall Effect
ignition system.
The PCM completely controls ignition system. During
crank/start mode, PCM will set a fixed amount of spark advance for an
efficient engine start. Amount of spark advance or retard is
determined by inputs that PCM receives from ECT sensor, engine vacuum
and engine RPM. During engine operation, PCM can supply an infinite
number of advance curves to ensure proper engine operation.
DISTRIBUTORLESS IGNITION SYSTEM (DIS)
DIS eliminates mechanical ignition components that can wear
out. PCM has complete ignition control and uses a coil pack, CMP
sensor and CKP sensor to control ignition timing. CMP sensor reads
slots in cam timing sprocket. PCM uses this information along with
information from CKP sensor to determine if fuel injectors and
ignition coils are properly sequenced for correct cylinders.
Basic timing is determined by CKP sensor position and is not
adjustable. One complete engine revolution may be required for PCM to
determine crankshaft position during cranking.
Molded ignition coils are used. Each coil fires 2 paired
spark plugs at the same time. One cylinder is on compression stroke
and other cylinder is on exhaust stroke.
HALL EFFECT IGNITION SYSTEM
This system is equipped with a Hall Effect distributor. See
Fig. 1 . Shutter(s) attached to distributor shaft rotate through
distributor Hall Effect switch, also referred to as a CMP sensor,
which contains a distributor pick-up (a Hall Effect device and
magnet). As shutter blade(s) pass through pick-up, magnetic field is
interrupted and voltage is toggled between high and low. PCM uses this
cylinder position data from CMP sensor, along with engine speed (RPM)
and CKP sensor data, to control ignition timing and injector pulse
width to maintain optimum driveability.
EMISSION SYSTEMS
Vehicles are equipped with different combinations of emission
system components. Not all components are used on all models. To
determine component usage on a specific model, see EMISSION
APPLICATIONS - TRUCKS article.
AIR INJECTION SYSTEM
This system adds a controlled amount of air to exhaust gases,
through air relief valve and check valves, to assist oxidation of
hydrocarbons and carbon monoxide in exhaust stream. Air is injected at
catalytic converters.
CRANKCASE VENTILATION (CCV) SYSTEM
CCV system performs same function as a conventional Positive

Crankcase Ventilation (PCV) system, but does not use a vacuum
controlled valve. See POSITIVE CRANKCASE VENTILATION (PCV).
EVAPORATIVE (EVAP) EMISSIONS SYSTEM
This system stores fuel vapors from fuel tank, preventing
vapors from reaching the atmosphere. As fuel evaporates inside fuel
tank, vapors are routed through vent hoses to charcoal canister where
they are stored until engine is started.
Evaporative Canister Purge Control Solenoid (EVAP-CPCS)
Charcoal canister purging is controlled by PCM through an
EVAP-CPCS. During engine warm-up and for a short period after hot
restarts, PCM energizes EVAP-CPCS, interrupting engine vacuum signal
to charcoal canister.
After engine reaches a predetermined operating temperature
and PCM internal timer has expired, PCM will de-energize EVAP-CPCS,
allowing engine vacuum to purge charcoal canister. EVAP-CPCS will also
be de-energized during certain idle conditions so PCM can update fuel
delivery calibration.
POSITIVE CRANKCASE VENTILATION (PCV)
PCV system uses a vacuum operated valve. A closed engine
crankcase breather/filter, with a hose connecting it to air filter
housing, provides source of air for system. Crankcase blow-by gases
are removed from crankcase through PCV valve with manifold vacuum.
These gases are introduced into incoming air/fuel mixture and become
part of the calibrated mixture.
A non-vacuum operated Crankcase Ventilation (CCV) system is
used on some engines, see CRANKCASE VENTILATION (CCV) SYSTEM.
SELF-DIAGNOSTIC SYSTEM
The PCM monitors several different circuits of engine control
system. If a problem is sensed with a monitored circuit, PCM will
store a Diagnostic Trouble Code (FTC) to aid technician in diagnosis
of system. The Malfunction Indicator Light (MIL), or a scan tool can
be used to read DTCs. For additional information, see SELF-DIAGNOSTICS
- JEEP, TRUCKS & RWD VANS article.
MALFUNCTION INDICATOR LIGHT
Malfunction Indicator Light (MIL) comes on and remains on for\
3 seconds as a bulb test each time ignition switch is turned to ON
position. If PCM receives an incorrect signal or receives no signal
from battery voltage input, charging system, ECT sensor, MAP sensor or
TP sensor, MIL will come on. MIL will also come on if certain
emission-related faults exist. This warns driver that PCM is in limp-
in mode and immediate repairs are necessary. See LIMP-IN MODE under
MISCELLANEOUS CONTROLS. MIL can also be used to display Diagnostic
Trouble Codes (DTCs). For additional information, see SELF-DIAGNOSTICS\
- JEEP, TRUCKS & RWD VANS article.
SERIAL COMMUNICATIONS INTERFACE (SCI)
SCI circuit is used by PCM to send data to and receive data
and sensor activation signals from scan tool. Scan tool uses signals
sent on SCI to display fault messages or Diagnostic Trouble Codes
(DTCs), sensor voltages and device states (On/Off). Scan tool uses S\
CI
to send solenoid and switch activation commands to PCM so that devices
and circuits can be tested. SCI is also used to write SRI mileage to

PCM.
MISCELLANEOUS CONTROLS
NOTE: Although not strictly considered part of engine performance
system, some controlled devices can adversely affect
driveability if they malfunction.
A/C CLUTCH RELAY
A/C clutch relay is controlled by PCM. When A/C or Defrost
mode is selected and PCM receives A/C request signal from evaporator
switch, PCM will cycle clutch on and off through A/C clutch relay.
When this relay is energized during engine operation, PCM will
determine correct engine idle speed through IAC motor.
When PCM senses low idle speed or wide open throttle through
TP sensor, PCM will de-energize A/C clutch relay, preventing A/C
operation.
AUTO SHUTDOWN (ASD) RELAY & FUEL PUMP RELAY
ASD relay and electric fuel pump relay are energized when
ignition is on. These relays are controlled through PCM by switching a
common ground circuit on and off. Following components are controlled
by ASD and fuel pump relays:
* Electric Fuel Pump
* Fuel Injectors
* Generator Field Winding
* Ignition Coil(s)
* HO2S Heating Element
When ignition switch is turned to RUN position, PCM energizes
ASD relay and electric fuel pump relay which powers these components.
If PCM does not receive a CMP and CKP sensor signal within one second
of engine cranking (start-up), PCM will turn ground circuit off and
de-energize ASD relay.
GENERATOR
Powertrain Control Module (PCM) regulates charging system
voltage.
LIMP-IN MODE
Limp-in mode is the attempt by PCM to compensate for failure
of certain components by substituting information from other sources
so that vehicle can still be operated. If PCM senses incorrect data or
no data at all from MAP sensor, TP sensor, ECT sensor or battery
voltage, system is placed into limp-in mode and Malfunction Indicator
Light (MIL) on instrument panel comes on.
If faulty sensor comes back on line, PCM will resume closed
loop operation. On some vehicles, MIL will remain on until ignition is
shut off and vehicle is restarted. To prevent damage to catalytic
converter, vehicle should NOT be driven for extended periods in limp-
in mode.
RADIATOR FAN RELAY
Electric cooling fan is used only on Dakota. Using
information supplied by A/C signal (if equipped), ECT sensor, and VSS,\

VEH IC LE C O M MUNIC ATIO N

1999 D odge P ic ku p R 1500
1999 ACCESSORIES & EQUIPMENT
CHRY - Vehicle Communications
Ram Pickup
IDENTIFYING VEHICLE COMMUNICATION PROBLEMS
Connect scan tool to Data Link Connector (DLC) to retrieve
messages. If scan tool message is blank, disconnect scan tool. Ensure
ground circuit has continuity at DLC terminal No. 4. Ensure 12 volts
exists at DLC terminal No. 16. Check power to DLC terminal No. 16 from
Power Distribution Center (PDC) fuse No. 12. Try another scan tool
and/or cable. If scan tool DTC or fault message is present, see
following bus fault messages list and proceed to appropriate DTC or
fault message:
* BUS (+) & BUS (-) OPEN
* BUS (+) OPEN
* BUS (-) OPEN
* BUS (+) & BUS (-) SHORTED TOGETHER
* BUS BIAS LEVEL TOO HIGH
* BUS BIAS LEVEL TOO LOW
* NO BUS BIAS
* NO RESPONSE AIR BAG CONTROL MODULE
* NO RESPONSE CENTRAL TIMER MODULE
* NO RESPONSE INSTRUMENT CLUSTER
* NO RESPONSE POWERTRAIN CONTROL MODULE
* NO RESPONSE COMPASS/MINI-TRIP SYSTEM
* NO RESPONSE RADIO
* NO TERMINATION
* NOT RECEIVING BUS MESSAGES CORRECTLY
* BUS SHORT TO 5 VOLTS
* BUS SHORT TO BATTERY
* BUS SHORT TO GROUND
BUS (+) & BUS (-) OPEN, (BUS (+) OPEN OR BUS (-) OPEN)
NOTE: For connector terminal identification and wiring diagrams,
see BODY CONTROL COMPUTER - INTRODUCTION article. Perform
VERIFICATION TEST VER-1 after each repair.
CAUTION: Always turn ignition off prior to disconnecting any module
connector.
1) Disconnect scan tool. Ensure ignition is on. Using an
external voltmeter, measure voltage between ground and DLC terminal
No. 3 (Violet/Brown wire). If voltage is not 1.8-2.3 volts, go to step\
3). If voltage is 1.8-2.3 volts, go to next step.
2) Measure voltage between ground and DLC terminal No. 11
(White/Black wire). If voltage is not 1.8-2.3 volts, go to next step.
If voltage is 1.8-2.3 volts, replace scan tool cable or scan tool.
3) Connect jumper wire between ground and DLC connector
terminal No. 11 (White/Black wire). Turn ignition off. Remove
instrument cluster. Using external ohmmeter, measure resistance
between ground and instrument cluster connector C1 terminal No. 9
(White/Black wire). If resistance is less than 5 ohms, go to next
step. If resistance is 5 ohms or more, repair open White/Black wire.
4) Disconnect jumper wire. Connect jumper wire between ground
and DLC connector terminal No. 3 (White/Black wire). Measure

CAUTION: Always turn ignition off prior to disconnecting any module
connector.
1) Remove and inspect fuse No. 11 from junction block.
Junction block is on left side of instrument panel. If fuse is open,
go to next step. If fuse is okay, go to step 3).
2) Using external ohmmeter, measure resistance between ground
and fused ignition switch output run/start terminal (Dark Blue/White
wire) on fuse No. 11 socket. If resistance is less than 5 ohms, repair
short to ground in Dark Blue/White wire. Replace fuse No. 11. If
resistance is 5 ohms or more, replace fuse No. 11.
3) Install fuse No. 11. Remove and inspect fuse No. 6 from
junction block. If fuse is open, next step. If fuse is okay, go to
step 5).
4) Using external ohmmeter, measure resistance between ground
and fused ignition switch output run/accy terminal (Dark Blue wire) on\
fuse No. 6 socket. If resistance is less than 5 ohms, repair short to
ground in Dark Blue wire. Replace fuse No. 6. If resistance is 5 ohms
or more, replace fuse No. 6.
5) Install fuse No. 6. Disconnect Central Timer Module (CTM)\
.
CTM is located under left side of instrument panel. Using external
ohmmeter, measure resistance between ground and CTM 18-pin connector
terminal No. 3 (Black/Orange wire). If resistance is more than 5 ohms,\
repair open Black/Orange wire. If resistance is 5 ohms or less, go to
next step.
6) Measure resistance between ground and CTM 14-pin connector
terminal No. 6 (Black/Light Green wire). If resistance is more than 5
ohms, repair open Black/Light Green wire. If resistance is 5 ohms or
less, go to next step.
7) Turn ignition on. Using scan tool, perform CCD Bus test.
Connect jumper wire between ground and CTM 18-pin connector terminal
No. 16 (Violet/Brown wire). If scan tool does not display BUS SHORT TO\
GROUND, repair open Violet/Brown wire. If scan tool displays BUS SHORT
TO GROUND, go to next step.
8) Disconnect jumper wire. Connect jumper wire between ground
and CTM 18-pin connector terminal No. 17 (White/Black wire). If scan
tool does not display BUS SHORT TO GROUND, repair open White/Black
wire. If scan tool displays BUS SHORT TO GROUND, replace CTM.
NO RESPONSE INSTRUMENT CLUSTER
NOTE: For connector terminal identification and wiring diagrams,
see BODY CONTROL COMPUTER - INTRODUCTION article. Perform
VERIFICATION TEST VER-1A after each repair.
CAUTION: Always turn ignition off prior to disconnecting any module
connector.
1) Turn ignition on. Using scan tool, select BODY CONTROL
MODULE. If scan tool displays NO RESPONSE, go to NO RESPONSE CENTRAL
TIMER MODULE. If scan tool does not display NO RESPONSE, go to next
step.
2) Using scan tool, select SYSTEM TEST. If scan tool displays
PCM ACTIVE ON THE BUS, go to next step. If scan tool does not display
PCM ACTIVE ON THE BUS, go to NO RESPONSE POWERTRAIN CONTROL MODULE.
3) Turn ignition off. Remove instrument cluster. Turn
ignition on. Using scan tool, turn on CCD bus bias under SYSTEM
MONITORS, then CCD BUS VOLTAGE. Connect jumper wire between ground and
instrument cluster connector C1 terminal No. 10 (Violet/Brown wire).
If scan tool voltage did not drop to about zero volts, repair open
Violet/Brown wire. If scan tool voltage dropped to about zero volts,
go to next step.

4) Move jumper to instrument cluster connector C1 terminal
No. 9 (White/Black wire). Monitor CCD BUS VOLTAGE. If scan tool
voltage did not drop to about zero volts, repair open White/Black
wire. If scan tool voltage did not drop to about zero volts, replace
instrument cluster.
NO RESPONSE POWERTRAIN CONTROL MODULE
NOTE: For connector terminal identification and wiring diagrams,
see BODY CONTROL COMPUTER - INTRODUCTION article. Perform
VERIFICATION TEST VER-1 after each repair.
CAUTION: Always turn ignition off prior to disconnecting any module
connector.
1) If engine does not run, see appropriate BASIC DIAGNOSTIC
PROCEDURES article in ENGINE PERFORMANCE section. If engine runs, go
to next step.
2) Turn ignition off. Disconnect Powertrain Control Module
(PCM). PCM is mounted in right side of firewall. Turn ignition on.
Connect jumper wire between ground and PCM connector C3 terminal. No.
30 (Violet/Brown wire). Using scan tool, perform CCD BUS test. If scan\
tool does not display SHORT TO GROUND, repair open Violet/Brown wire.
If scan tool displays SHORT TO GROUND, go to next step.
3) Move jumper wire to PCM connector C3 terminal No. 28
(White/Black wire). Perform CCD BUS test. If scan tool does not
display SHORT TO GROUND, repair open White/Black wire. If scan tool
displays SHORT TO GROUND, replace PCM.
NO RESPONSE COMPASS/MINI-TRIP SYSTEM
NOTE: For connector terminal identification and wiring diagrams,
see BODY CONTROL COMPUTER - INTRODUCTION article. Perform
VERIFICATION TEST VER-1 after each repair.
CAUTION: Always turn ignition off prior to disconnecting any module
connector.
1) Remove and inspect fuse No. 11 from junction block.
Junction block is on left side of instrument panel. If fuse is open,
go to next step. If fuse is okay, go to step 3).
2) Using external ohmmeter, measure resistance between ground
and fused ignition switch output run/start terminal (Dark Blue/White
wire) on fuse No. 11 socket. If resistance is less than 5 ohms, repair
Dark Blue/White wire for short to ground. Replace fuse No. 11. If
resistance is 5 ohms or more, replace fuse No. 11.
3) Reinstall fuse. Disconnect CMTC 12-pin connector. Turn
ignition on. Using external voltmeter, measure voltage between ground
and CMTC connector terminal No. 1 (Dark Blue/White wire). If voltage
is less than 9.5 volts, repair open Dark Blue/White wire. If voltage
is 9.5 volts or more, go to next step.
4) Using external voltmeter, measure voltage between ground
and CMTC connector terminal No. 5 (Pink wire). If voltage is less than\
9.5 volts, repair open Pink wire. If voltage is 9.5 volts or more, go
to next step.
5) Turn ignition off. Using external ohmmeter, measure
resistance between ground and CMTC connector terminal No. 7
(Black/Light Green wire). If resistance is 5 ohms or less, go to next
step. If resistance is more than 5 ohms, repair open Black/Light Green
wire.
6) Using scan tool, perform CCD bus test. Connect jumper wire
between ground and CMTC connector terminal No. 2 (Violet/Brown wire).
If scan tool displays BUS (+) SHORTED TO GROUND, go to next step. If

scan tool does not display BUS (+) SHORTED TO GROUND, repair open
Violet/Brown wire.
7) Move jumper wire to CMTC connector terminal No. 8
(White/Black wire). If scan tool displays BUS (+) SHORTED TO GROUND,\
replace CMTC. If scan tool does not display BUS (+) SHORTED TO GROUND,\
repair open White/Black wire.
NO RESPONSE RADIO
NOTE: For connector terminal identification and wiring diagrams,
see BODY CONTROL COMPUTER - INTRODUCTION article. Perform
VERIFICATION TEST VER-1A after each repair.
CAUTION: Always turn ignition off prior to disconnecting any module
connector.
1) If radio screen is not blank, go to step 7). If radio
screen is blank, go to next step.
2) Remove and inspect junction block fuse No. 8 (radio). If
fuse is blown, go to next step. If fuse is okay, go to step 4).
3) Turn ignition off. Disconnect radio Gray connector. Using
external ohmmeter, measure resistance between ground and radio Gray
connector terminal No. 6 (Red/White wire). If resistance is less than
5 ohms, repair Red/White wire for short to ground. Replace junction
block fuse No. 8. If resistance is 5 ohms or more, replace radio.
Replace junction block fuse No. 8.
4) Turn ignition on. Measure voltage between ground and
terminal No. 7 (Pink wire). If voltage is 10 volts or less, repair
open Pink wire. If voltage is more than 10 volts, go to next step.
5) Install fuse. Disconnect radio Gray connector. Using
external voltmeter, measure voltage between ground and radio Gray
terminal No. 6 (Red/White wire). If voltage is 10 volts or less,
repair open Red/White wire. If voltage is more than 10 volts, go to
next step.
6) Inspect ground strap and antenna for correct installation.
Repair as needed. If ground strap and antenna are okay, replace radio.
7) Disconnect 2-pin CCD BUS connector on back of radio.
Connect jumper wire between terminal No. 2 (White/Black wire) and
ground. Using scan tool, select BODY, BODY COMPUTER, then SYSTEM TEST.
Perform CCD BUS test. If scan tool does not display BUS SHORT TO
GROUND, repair open White/Black wire. If scan tool displays BUS SHORT
TO GROUND, go to next step.
8) Move jumper wire to terminal No. 1 (Violet/Brown wire).
Perform CCD BUS test. If scan tool does not display BUS SHORT TO
GROUND, repair open Violet/Brown wire. If scan tool displays BUS SHORT
TO GROUND, replace radio.
NO TERMINATION
NOTE: For connector terminal identification and wiring diagrams,
see BODY CONTROL COMPUTER - INTRODUCTION article. Perform
VERIFICATION TEST VER-1 after each repair.
CAUTION: Always turn ignition off prior to disconnecting any module
connector.
1) Disconnect Powertrain Control Module (PCM) connectors. PC\
M
is mounted in right side of firewall. Connect jumper wire between
ground and PCM connector C3 terminal No. 30 (Violet/Brown wire). Using\
scan tool, select SYSTEM MONITORS. Perform CCD BUS test. If scan tool
does not display BUS SHORT TO GROUND, repair open Violet/Brown wire.
If scan tool displays BUS SHORT TO GROUND, go to next step.
2) Move jumper wire to PCM connector C3 terminal No. 28

more, go to next step.
9) Measure resistance between ground and DLC connector
terminal No. 11 (White/Black wire). If resistance is less than 700
ohms, repair White/Dark Green wire for short to ground. If resistance
is 700 ohms or more, replace scan tool cable or scan tool as
necessary.
VERIFICATION TEST VER-1
1) Reconnect all previously disconnect connectors. Turn
ignition on, engine off. Using scan tool, erase all fault messages.
Turn ignition off. Wait 10 seconds. Turn ignition on, engine off.
Operate system that is malfunctioning. If system does not operate
properly, perform SYMPTOM IDENTIFICATION of BODY CONTROL COMPUTER
TESTS - RAM PICKUP article. If system operates properly, go to next
step.
2) Using scan tool, read fault messages. If fault messages
exist, perform SYMPTOM IDENTIFICATION of BODY CONTROL COMPUTER TESTS -
RAM PICKUP article. If fault messages do not exist, repair is
complete.